Insulin in serum

The reference values (norm) of serum insulin concentration in adults are 3-17 μED / ml (21.5-122 pmol / l).

Insulin is a polypeptide whose monomeric form consists of two chains: A (of 21 amino acids) and B (of 30 amino acids). Insulin is formed as a product of proteolytic cleavage of the insulin precursor, called proinsulin. Actually, insulin is formed after exiting the cell. Cleavage of the C-chain (C-peptide) from proinsulin occurs at the level of the cytoplasmic membrane, in which the corresponding proteases are enclosed. Insulin is necessary for cells to transport glucose, potassium and amino acids into the cytoplasm. It has an inhibitory effect on glycogenolysis and gluconeogenesis. In adipose tissue insulin enhances glucose transport and intensifies glycolysis, increases the rate of synthesis of fatty acids and their esterification and inhibits lipolysis. With prolonged action, insulin increases the synthesis of enzymes and the synthesis of DNA, activates growth.

In the blood, insulin reduces the concentration of glucose and fatty acids, as well as (albeit insignificantly) amino acids. Insulin comparatively rapidly breaks down in the liver under the action of the enzyme glutathione insulin transhydrogenase. The half-life of insulin, administered intravenously, is 5-10 minutes.

The cause of diabetes is insufficiency (absolute or relative) of insulin. Determining the concentration of insulin in the blood is necessary for differentiation of various forms of diabetes mellitus, the choice of a therapeutic drug, the selection of optimal therapy, and the establishment of the degree of β-cell insufficiency. In healthy people, when carrying out PTGT, the concentration of insulin in the blood reaches a maximum 1 hour after taking glucose and decreases after 2 hours.

The violation of glucose tolerance is characterized by a slowdown in the rise in insulin concentration in the blood relative to the rise in glycemia in the process of PTGT. The maximum increase in insulin levels in these patients is observed 1.5-2 hours after taking glucose. The content in the blood of proinsulin, C-peptide, glucagon in the normal range.

Diabetes mellitus type 1. The basal concentration of insulin in the blood is within the norm or reduced, observe a smaller increase in it during all the periods of PTGT. The content of proinsulin and C-peptide is reduced, the glucagon level is either within normal limits, or slightly elevated.

Diabetes mellitus type 2. With a mild form, the concentration of insulin in the blood on an empty stomach is slightly increased. In the course of PTGT, it also exceeds the normal values during all periods of the study. The blood content of proinsulin, C-peptide and glucagon has not been changed. In the form of moderate severity, an increase in the concentration of insulin in the blood on an empty stomach is revealed. In the process of PTGT, the maximum insulin release is observed at the 60th minute, after which a very slow decrease in its concentration in the blood occurs, therefore, a high insulin content is observed after 60, 120 and even 180 minutes after loading with glucose. The content of proinsulin, C-peptide in the blood is reduced, glucagon - increased.

Hyperinsulinism. Insulinoma is a tumor (adenoma), consisting of β-cells of pancreatic islets. The tumor can develop in people of any age, it is usually single, benign, but can be multiple, combined with ademotosis, and in rare cases - malignant. In the organic form of hyperinsulinism (insulinoma or nezidioblastoma) there is a sudden and inadequate production of insulin, which causes the development of hypoglycemia, usually paroxysmal. Hyperproduction of insulin does not depend on glycemia (usually above 144 pmol / l). The ratio of insulin / glucose is more than 1: 4.5. Often there is an excess of proinsulin and C-peptide on the background of hypoglycemia. The diagnosis is not in doubt, if the level of insulin in the plasma is higher than 72 pmol / l against a background of hypoglycemia (blood glucose concentration less than 1.7 mmol / l). As a diagnostic sample, loads of tolbutamide or leucine are used: in patients with insulin-producing tumors, there is often a high rise in insulin concentration in the blood and a more marked decrease in glucose levels compared to healthy ones. However, the normal nature of these samples does not exclude the diagnosis of a tumor.

Many types of malignant tumors (carcinomas, especially hepatocellular, sarcomas) lead to the development of hypoglycemia. Most often hypoglycemia accompanies tumors of mesoderm origin, resembling fibrosarcomas and localized primarily in the retroperitoneal space.

Functional hyperinsulinism often develops in various diseases with impaired carbohydrate metabolism. It is characterized by hypoglycemia, which can occur against the background of unchanged or even elevated insulin concentrations in the blood, and hypersensitivity to the insulin administered. The samples with tolbutamide and leucine are negative.

Diseases and conditions in which the concentration of insulin in the blood changes

Insulin is raised

• Normal pregnancy
• Diabetes mellitus type 2 (onset of the disease)
• Obesity
• Diseases of the liver
• Acromegaly
• Isenko-Cushing syndrome
• Muscular dystrophy
• Insulinoma
• Family intolerance to fructose and galactose

Insulin reduced

• Prolonged physical activity
• Diabetes mellitus type 1
• Diabetes mellitus type 2

[1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11]